Thanks for the suggestions. I already added a 0.1uf miflex with the 9uf sonicap on the tweeter circuit. Does the 3.6uf cap need to be 250v? Looking to spend about 100$. The miflex would be way outside my budget.
Just an FYI, that 3.6uF cap is used in a notch filter.
That's probably the last place I would use a copper foil capacitor.
It's main purpose is to reduce output within a narrow frequency band.
So while a signal is technically passing through it, you're not going to gain anything by going with higher quality capacitor
As it's intended use is both narrowly focused and "subtractive"
Personally, I would put the money into upgrading the main resistor to a path or Duelund CAST resistor.
Alternatively, adding a high quality bypass capacitor to the midrange bundle, and bypass to the cap in shunt at the end of the network where the effect will be most beneficial as they affect the main cap provides is additive.